The present invention relates to magnetic disc storage systems. More specifically, the present invention relates to a system for dithering heads in a magnetic disc storage system.
Magnetic disc storage systems are used to magnetically store information. Typically, a storage system includes a number of discs, each side of which carry magnetically coded information. The information on the disc is read and written using magnetic heads which are carried on the end of the actuator arms. Both thin film inductive heads and magnetoresistive (MR) heads are used in disc drives. Information is carried on the disc in the form of data residing on tracks which are divided into sectors. Tracks are also referred to as cylinders.
Information is written to or read from the disc by positioning a magnetic head over a desired cylinder of a desired disc. The disc spins at a high speed and the head therefore moves relative to the surface of the disc. Rotation of the disc relative to the head provides a lifting force on a slider body which carries the head. The head is an extremely delicate component and "flies" (due to the lifting force) very close to the disc surface. This causes a number of design problems, primarily wearing of the head due to occasional and accidental contact with the disc surface.
During periods of inactivity, some disc drives have attempted to control the radial position of the head to achieve desirous results. Specifically, it has been known to "dither" the head over the cylinders which yield the highest fly height thereby reducing wear of the head due to contact with the disc surface. Additionally, the dithering can be tuned to reduce power consumption by limiting movement to those cylinders which require less power to maintain flight of the head. Dithering is used because it is impractical and would result in excessive wear to spin down the disc during short periods of inactivity. At the same time, simply leaving the head flying at its most recent track could lead to wear and increased power consumption. However, the prior art has failed to recognize and fully utilize the benefits that can be achieved through dithering.